Not able to run the subroutine ……..error is coming ……UMAT: illegal (negative) actual void ratio detected
Can anybody help
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Hi, so I guess you provided illegal (negative) actual void ratio 🙂
Hypoplasticity is porosity-dependent model and proper initialisation of state variables is needed, either through sdvini, or through the initialisation implemented directly in umat routine (this is not available in all umats, depends on what umat you use). For example, in sand hypoplasticity umat
https://soilmodels.com/download/plaxis-umat-hypoplas-tar-gz/
you can initialise void ratio using parameter 16, so sdvini routine is not needed, see
https://web.natur.cuni.cz/uhigug/masin/plaxumat/node5.html
I used the model parameters from the Ex-calibre database for sand hypoplasticity (dobrany) and initial (actual) void ratio as the one before oedometric test (0.996). And I’m getting the error for negative actual void ratio. Am I doing something wrong or there could be other reasons for this error?
Hi Jasmine, to try to find out where is the problem, I suggest you to run umat in element test program first. You can also try different sand model umat (there are more options at SoilModels).
Thank you Professor for your prompt reply. I figured from the .dat file in ABAQUS that the void ratio value given in the sdvini subroutine has not been somehow considered in the analysis, because the value printed is null.
I could run the element tests (triaxial) using the subroutines. But, when I open the input file in ABAQUS and then try to run it, it gives error of void ratio.
Thanks got it……..I am using ABAQUS….Is any documentation is available for ABAQUS………I have checked for plaxis well documented manual is there…..Is it possible check pore water pressure and damping during earthquake (forABAQUS)………Currently I am using UMAT the one available in the link https://soilmodels.com/download/plaxis-umat-hypoplas-tar-gz/ (for abaqus i am using only umat file)
The description on parameters here:
https://web.natur.cuni.cz/uhigug/masin/plaxumat/node5.html
is valid both for Plaxis and Abaqus.
If you want to run undrained analysis, then bulk modulus of water Kw is at parameter 15 and excess pore water pressure at statev 8. The same as in clay model (par7, statev8):
https://web.natur.cuni.cz/uhigug/masin/plaxumat/node6.html
Thank you very much……what is the unit of input and output state variable parameter……….can the model be used for liquefaction assessment …….. any limitation i am thinking of using it……….
in page no 6 of documentation it is written as state variable 8 is not used
Hi, yes, I know it is written, but I kept it for internal purposes, it is used. I will correct it in documentation later on. As for liquefaction, in principle you can use it, but this will be up to you, to calibrate the model using your data and assess predictive capabilities. As for state variables, there are either no units or kPa, but this will also be up to you to go through documentation… Hope the model helps, regards David
thank you very much